Opponents of open source often use the specter of potential patent infringement charges to protect their proprietary turf.

Questions over patent validity in software are never easy to answer, but it's one that a new effort called Linux Defenders from the Open Invention Network (OIN) is trying help solve.

Linux Defender includes facilities for peer-to-peer patent review, post patent review as well as defensive publications for patents.

With Microsoft alleging, or just hinting strongly in some cases, that open source technologies infringe on over 200 Microsoft patents , the new effort might potentially help open source and Linux vendors to defend themselves should the need arise.

But the overall goal of Linux Defenders is to ensure that patents are of high quality and that prior art is properly recognized in the patent process.

"It's not really focused on Microsoft," Keith Bergelt, chief executive officer of Open Invention Network told InternetNews.com. "Under post-issue Peer to Patent there will probably be some Microsoft patents up there, there will probably be some from small companies and trolls, he said, using a pejorative term for patent-holders who often manipulate the patent system for excessive profits.

It really will be a mixture, but I don't think you should expect to see 30 Microsoft patents up there. We don't have Microsoft patents up there now."

A Microsoft spokesperson was not immediately available for comment on the new service. Since claiming in 2007 that open source technologies infringed on its patents, Microsoft has softened its tone. At a 2008 open source event, Sam Ramji, Microsoft's director of open source technology strategy, told attendees that Microsoft has never litigated against open source users. But the issues that arise between patented software and open source creations remain in place.

As part of the Linux Defender program, the OIN will look at issued patents in an effort called the post issue Peer to Patent effort. If warranted, the OIN would help challenge an already issued patent if it believes it is invalid based on information it has or is made aware of by the open source community.

The Linux Defender effort will also do peer review of pending patent publications in an effort to help validate that a patent application is non-obvious and has not already been invented.

Linux Defender will also engage in a practice known as Defensive Publications. A Defensive Publication is a set of documents that describes a production or method, which could then become a source for defining prior art in the patent awarding process. Applicants for U.S. Patents are expected to show that their invention is obvious and original. The Linux Defender Defensive Publications effort is an attempt to identify everything that has already been invented by open source and Linux technologies.

Bergelt described the Linux Defender Defensive Publication initiative as a tool for helping with future patent claims. For example, if an invention has a Defensive Publication filed with it, then a future patent application from a third party could be potentially be invalidated. After all, Bergelt noted, Prior art is dependent on chronology in most instances, such that whoever published first.

Bergelt admitted that a Defensive Publication could also be used to help out with a patent that potentially has already been granted. In such case the original inventor might not have formally published a defensive publication prior to a patent have been granted.

"There are situations where the defensive publication itself would not serve as prior art," Bergelt explained. "But for that patent at issue as long as we can prove the earliest publication, not as a defensive publication but in an informal structure whether in a presentation or in a website we can show where it came from and when it was first made available in the public domain. Then we could take it back as part of the post patent effort for re-examination."

Bergelt noted that while the open source community has been good at developing innovation, it hasn't always been as good at codifying that innovation from a legal perspective. Though larger companies like IBM, Red Hat and Novell have been able to patent some of their open source innovations, Bergelt argued that smaller companies and projects have been boxed out of the process.

Could Linux Defender balance the playing firled? It's one of the goals.

The OIN itself was formed in 2005 as a multi-vendor effort to provide royalty-free usage of patents to open source project. As such Bergelt sees the Linux Defender effort as a natural extension of what OIN has already been doing.

"We want to provide a single source for people in the open source community and especially Linux as a path to affecting change," Bergelt said.